We plan to continue our investigation of the interaction of large charged bodies as a function of their separation. In the last three years we have introduced a simple approximation based upon the statistical mechanics of ionic solutions and have used it to calculate the thermodynamic properties of real electrolytes, potentiometric titration data of spherical and cylindrical polyelectrolytes, and the interaction between two large charged spheres immersed in an aqueous solution of simple electrolyte. This last problem is central to the classical theory of colloid stability. Parallel to this simple approximation, we intend to reformulate several other statistical theories and to push them to the limit in which the ration of the ionic sizes and the ratio of the charges differ appreciably from unity. It is necessary to do this for several theories since there are no a priori criteria which assure superiority of any one approach. We expect to be able to do this without a great deal of computational effort since we have recently developed variational principles for a number of these theories and so shall be able to solve them more readily than by lengthy iterative methods. We plan to develop reliable theories of the electrical double layer about a spherical ion and planar surface which include the effects of ionic size, an important and well-known deficiency of the Poisson-Boltzmann equation. In addition to the obvious application of the interaction of spherical double layers, we plan to undertake a serious theoretical study of the interaction between two charged planar surfaces, a system that has recently been studied experimentally by two quality research groups and for which there are clear deviations from classical colloid theory. This will lead us back to introduce more appropriate and more general boundary conditions than have normally been used in statistical mechanics since the surfaces in the above studies do contain ionizable groups which respond to their local ionic environment, and so the surface charge and surface potential are not fixed, but most likely vary with the separation between the planes. We then intend to introduce these boundary conditions into the two-sphere problem and hopefully have a rather complete and reliable theory that is valid for all relevant electrolyte concentrations.